Without being able to view your return, it's impossible to say exactly what caused your refund to decrease. However, there's a high probability that at least one reason is listed below.
If your refund is wildly off, it's possible you simply mistyped a dollar amount somewhere. An extra digit here, a missing number there, even something as seemingly insignificant as a misplaced decimal point can have an eye-popping effect on your TurboTax refund.
Changes in your income or tax rate
My income only increased by $2898. My W-4 did stay the same, but would a $2898 increase in salary really effect my return that much? Other than that slight change in salary, I have had zero changes from last year.